X-ray display panel

ABSTRACT

An improved x-ray display panel is disclosed wherein the x-rays forming the pattern to be displayed induce &#39;&#39;&#39;&#39;ionizing events&#39;&#39;&#39;&#39; over the surface of the panel. The photon producing discharges as a result of these events make up a visible image of the x-ray pattern.

Nov. 6, 1973 United States Patent 1 1 Webster VRV T T 9L9 676 l /0/ 5551 1 3 3 L'Heureux .11.. 313/108 A Charpak et a1. 250/71 R vlm m mm m mwn yr 3 H62 m h u.mue CDBTTB 700 37 65777766 99999999 HHHHHHHH 003469000 99906733 6239 303 ,33 1 2 40994377 30050000 32333333 H CY S .WN mw my n A 1 P F U 1 Me 6 M Y m In 2 9 A 0 e e i L r n 5 P a MC u 6 S H (Sa 2 I J D E C 0 Y m m N A .W m .L R w c w n H X1 A F A 1. 1 1 4 5 3 2 15 7 7 2 2 II I ll Related US. Application Data Primary ExaminerRonald L.Wibert Continuation-impart of Ser. No. 97,916, Dec. AssistantExaminer-Ronald Stem 1970, abandoned. Att0rneyJohn F. Ahern et a1.

ray display panel is disclosed wherein the trays forming the pattern tobe displayed induce T C A R T S B A X 0 e V 0 r P ].m 7 n BA 60 4 R67353 .00 31 ,0 RHm 00 7 0M l O /l8 3 1 9 2 0G.

5 a 1mm mmhh c n.r ."a a "us 1 2 I s h U.mF .11.] 218 555 [1:1

315/169 TV, 246; 313/89, 94, 101, 108 R,

anizing events over the surface of the panel. The

photon producing discharges as a result of these events [56] ReferencesCited make up a visible image of the x-ray pattern.

UNITED STATES PATENTS 17 Claims, 6 Drawing Figures 3,579,015 5/1971Gregory....................... 315/169 TV 6'000039 1000 00000000 0OOJC@90 0 000 0O0.m0000@@ 00 000%000 D090fl00 00. 10 0008 1016 PATENTEUnnv 6I973 INVENTOR HAROLD F. WEBSTER BY W G. will;

HIS ATTORNEY 1 X-RAY DISPLAY PANEL BACKGROUND OF THE INVENTION Thisapplication is a continuation-in-part of application Ser. No. 97,916,filed Dec. 14, 1970, now abandoned.

THE DISCLOSURE This invention relates to display panels and particularlyto a display panel for converting an x-ray image to visible light.

At present, x-ray images are viewed on fluoroscopes comprising a specialphosphor screen sensitive to xrays. These phosphors are relativelyinefficient and the image produced thereby is rather dim.

Previous attempts to improve the operation of fluoroscopes generallyfall into one or the other of two categories: either attempts are madeat increasing the phosphor efficiency or an image intensifier is used.An image intensifier, for example, may comprise a phosphor layer plus aphotoelectric surface upon which the image falls. Light from thephosphor liberates electrons from the photoelectric surface which areaccelerated in an electric field and caused to strike a second phospherscreen, yielding a much brighter image due to the increased energy ofthe electrons.

Each of these techniques has a number of drawbacks. Phosphor efficiencycan only be increased a limited amount, i.e.,.energy conversiontechniques are limited by the. amount of input energy. The problem isnot so much with the phosphor as with the radiation limits'imposed. Thatis, the image could easily be made brighter by increasing the x-raydosage. This, however,creates increased radiation hazards for thesubject and for the operator. Thus, one, is restricted to a low levelradiation source and faced with the fact that energy conversiontechniques will never achieve one hundred percent efficiency.

Image intensifiers, while beneficial in many respects, tend to berelatively expensive and restricted in size. The size restrictionresults from the electric field necessary to accelerate the electrons;the larger the field, the more difficult it is to generate. Thus, thearea viewed with an image intensifier is smaller than that provided by afluoroscope alone.

In or about 1966, a gaseous display and memory panel was developed atthe University of Illinois for use as a graphic output device fordigital computers. Te Illinois panel comprises a central glass platehaving an array of holes arranged in regular rows and columns Thegenesis of this invention was the heretofore un disclosed realizationthat by making certain modifications in the operating parameters of theabove described Illinois display panel, an improved x-ray display panelmay be provided. Moreover, this invention includes the heretoforeundisclosed realization that simplifying structural modifications to theprior art Illinois display panel can be advantageously made in animproved x-ray display panel. Specifically, if the elec trodes of anIllinois panel are simultaneously, in parallel, connected across asource of electrical potential whose magnitude is not sufficient aloneto cause breakdown across the perforated plate, such breakdown may beselectively stimulated by radiation thereby providing a radiation imagedisplay panel. Secondly, the structure can be modified by replacing theplurality of stripe electrodes on each outer plate of the Illinois panelwith a single electrode of large area on each outer plate. Thissimplifies the fabrication of the required electrodes and eliminates theneed for registration thereof with the perforations in the centralplate.

In view of the foregoing, it is therefore an object of the presentinvention to provide a bright 'x-ray image screen.

It is a further object of the present invention to provide a brightx-ray image screen capable of being made in any desired size.

Another object of the present invention is to provide an image displaywherein the input. signal is used as a control signal rather than merelybeing converted to a visible form of energy.

A further object of the present invention is to provide an image displaypanel wherein the incident radiation provides an ionizing event withinthe panel thereby generating a visible electric discharge.

The foregoing objects and other advantages are achieved by the presentinvention wherein there is provided adisplay panel comprising parallel,spaced, electrically conducting radiation transmitting plates separatedby a perforated plate. The spaced plates are connected to a source ofhigh voltage. As x-ray's strike the display panel, an x-ray emittedelectron in the region of a hole in the perforated central plate causesa discharge through the hole resulting in a bright visible dot. TI-leregion between the two outer plates is enclosed and filled with anysuitable gas or mixture of gases; for example, neon or xenon.

A more complete understanding of the present invention may be obtainedby considering the following detailed description in connection with theattached drawings in which:

FIG. 1 is an exploded view illustrating the overall arrangement of adisplay panel in accordance with the stripe electrodes on the secondouter glassplate, a gaseous discharge in one hole of the central glassplate is produced responsive to the computer output word. The gaseousdischarge produces a point of light whose posi: tion in the array ofholes in the central glass plate conveys a quantum of output informationfrom the computer.

present invention.

FIG. 2 illustrates a side view, on a much larger scale, of a portion ofthe display panel. I

FIG. 3 illustrates a modification of the present tion. FIG. 4illustrates another modification of the present invention. ,l v

FIG. 5 illustrates the operation of the present invention.

FIG. 6 illustrates an alternative mode of operation Referring to FIG. 1,there is illustrated the overall ar invenrangement of display panel 10in accordance with the I present invention. Display panel 10 comprises afirst outer radiation transmissive plate 11 having deposited thereon acoating 12 thereby making a transparent electrode. A second outerradiation transmissive plate 13 has deposited thereon a conductive layer14 making a second transparent electrode. Plates 11 and 13 may,

for example, be glass, a polycarbonate plastic such as LEXAN (atrademark of General Electric Company) or other material having similarfluid-impervious radiation transmissive characteristics. Electrodes 12and 14 may, for example, be films of a metal oxide such as tin oxide.Alternatively, a first electrode 12 which receives the x-ray energy fromwhich an image is to be formed, may be a metallic electrode and may toadvantage be a thin gold foil electrode; in either case electrode 14 ispreferably a metal oxide film. Spaced between the two outer plates andseparated therefrom by a small distance is a perforated plate 15containing an array of holes 16. The arrangement of holes 16 may beeither random or in a pattern. It is preferred to have them in a patternsince the number of holes per unit area can be increased thereby. It ispreferable to form the perforated plate of a dark-colored material inorder to minimize reflection of room light and to maximize displaycontrast.

In operation, display panel 10 is either inserted into a suitablecontainer or the volume contained within the outer plates sealed so thata suitable gas may be contained within the volume defined by the outerplates. For maximum display brightness, the gas is preferably either amixture of a gas selected from the group consisting of nitrogen andhydrogen and a gas selected from the group consisting of helium, argon,and neon at a pressure of between one-half and l atmoshpere, oralternatively, pure xenon at a pressure of approximately one-halfatmosphere. A source of potential, which may be either a-c or d-c isapplied to electrode surfaces 12 and 14. In a first example of apreferred embodiment of this invention, the gas employed was anitrogen-neon mixture and a voltage of approximately 600 peak RF voltsat various frequencies in the range 38 to 120 kilohertz was appliedbetween electrodes 12 and 14. The RF voltage was pulsed with cycles of33 millisecond on-times and l to 3 millisecond off-times. During theoff-times, any x-ray excited discharges in the perforations of thecentral plate are extinguished thereby providing for real-time dynamicx-ray display. In a second example, pure xenon gas was employed and a300 volt d-c potential was applied between electrodes 12 and 14. Whenx-rays, for example, from source 20 irradiate an object such as sphere21, a shadow will be cast upon the display panel as illustrated bycircular pattern 22. As the x-rays strike the panel, they act as anionizing event" and serve to initiate a discharge within holes 16 of thearray of the central plate 15. This is described in more detail withreferences to FIGS. 2-4.

In accordance with an important feature of this invention, xenon is thepreferred gas for filling the discharge cells comprising theperforations of the perforated central plate. Xenon is a heavy gas andaccordingly absorbs x-rays well, emitting photoelectrons in response tothe x-rays absorbed. The photoelectrons emitted are accelerated by theelectric field maintained between electrodes 12 and 14 and typicallycollide with other xenon atoms which in turn emit secondaryphotoelectrons and so on in an avalanche effect. The providing of suchavalanche effect is important in practicing this invention, because themore readily initiated ava-v lanche in the heavy gas, xenon, increasesthe sensitivity of the triggering of the discharge cells by x-rays. Thisis important to the functioning of an x-ray display panel, whereas incontrast, it is not important to the functioning of a computer read-outpanel such as the Illinois panel since, in the case of the read-outpanel, triggering can be assured by simply increasing the electricalpotential applied across the discharge cells.

FIG. 2 illustrates a section of display panel 10 specifically concerningthe region around one of the holes 16 in array. Holes 16 may be obtainedin any suitable fashion, however, in order to generate a large number ofholes of relatively small size, resort may be made to the radiationdamage etch technique developed by the General Electric Company. When anx-ray, symbolized by the arrow 17, enters the display panel throughouter plate 11, an electron is emitted and drifts into the hole region16. The presence of electrons in the hole region induces an electricdischarge between conductive layers 12 and 14. This electric dischargethen produces visible light symbolized by the arrow 18. A viewer lookingat the entire display panel would then see a pattern formed by the x-rayimage in the form of a very large number of small dots of light notunlike a black and white image formed on a color television tube. All ofthe plates utilized in display panel 10 should be relatively opaque toultraviolet radiation to prevent the accidental triggering of thedisplay panel by room lights or the electrical discharge in adjacentholes within central plate 15.

FIG. 3 illustrates a modification of the present invention wherein athin layer 19 ofa relatively heavy refractory metal is deposited overconductive layer 12 on the inside of objective plate 11, that is, theplate facing the source of the x-ray image. This layer of heavyrefractory metal 19, which may for example be a very thin layer of lead,serves to increase the yield of photoelectrons and thus the sensitivityof the display panel 10 to an x-ray image. A similar result may also beobtained by making outer plate 11 ofleaded glass, or by making electrode12 itself of a metal foil. Gadolinium, lead, and gold have been found tobe in that order, suitably efficient sources of x-ray stimulatedphotoelectrons. Accordingly, electrode 12 may advantageously begadolinium foil or lead foil. Gadolinium is more efficient in producingx-ray stimulated photoelectrons, but lead is less expensive. The choiceof the preferred material is therefore a design trade-off.

FIG. 4 illustrates a further modification of the present inventionwherein a layer of phosphor 30 is applied over conductive layer 12 onthe objective plate. The phosphor layer 30 converts the x-rays toultraviolet photons thereby increasing the sensitivity of display panel10 to an x-ray image. The additional photons obtained by themodifications of FIGS. 3 and 4 act to increase the ionizing eventswithin a hole 16 and serve to more readily cause an electric dischargethereby producing the visible image.

In FIG. 5 there is illustrated the over-all operation of an x-raydisplay panel in accordance with the present invention. when .anionizing event takes place within a hole-region 16, discharge occursbetween conductive plates 12 and 14. The energy for this discharge issupplied by a power source symbolized by battery 23 which is coupled toconductive layers 12 and to conductive layer 14 by wayof seriesresistance 24. Series resistance 24 serves a current limiting'functionto prevent runaway within the display panel. It has been found' that,with this relatively simple configuration, a discharge within holeregion 16 may tend to increase the voltage drop across series resistance24 and inhibit discharges within other hole regions. The net effect isto tend to make the discharge occur sequentially rather thansimultaneously.

Apparatus for overcoming the sequential discharge is illustrated in FIG.6 wherein series resistance 24 has been replaced by what amounts to aplurality of parallel resistances connected one to each hole region.Specifically, the plurality of resistances preferably takes the form ofa resistive coating overlying conductive plate 14. Suitable materialsfor resistive layer 25 are ruthenium oxide, such as sold by AlloysUnlimited, Inc. under the trade name R l7A resistive paste, orcobaltsilicon organo metallic solution, such as sold by EngelhartIndustries. In the operation of FIG. 6, an ionizing event will induce adischarge within hole region 16. However, since each hole region iseffectively connected to source 23 by its own resistor, the increase involtage drop across each individual resistor is not coupled to theremaining resistors of the display panel. The

result is then a simultaneous discharge of those regions in which anionizing event has been described and illustrated, it will be apparentto those skilled in the art that many modifications can be made withoutdeparting from the spirit and scope of the present invention.

The invention claimed is:

I. In a radiation imaging system including a source of radiation forirradiating an object to be imaged and radiation detecting display meansreceiving radiation which has interacted with said object, an improvedradiation detecting display panel comprising:

first and second radiation transmissive fluid impervious plates orientedgenerally parallel to one an other and spaced apart;

a continuous unitary conductive coating applied over substantially theentire area of the interior surfaces of each of said plates to formfirst and second electrodes, at least one of said electrodes being lighttransmissive;

a plate having generally cylindrical voids therein extendingtherethrough for the entire thickness thereof placed between andgenerally parallel with said electrodes;

enclosure means for sealing in gas-containing relationship at least theregion between said first and second plates and for containing a gastherein;-and

a source of electrical potential coupled to saidfirst and secondelectrodes and producing an electric field therebetween.

2. An improved radiation detecting display panel as set forth in claim 1wherein one of said electrodes comprises a metal oxide film.

3. The display panel of claim 2 wherein said metal oxide film comprisestin oxide.

4. The display panel of claim 2 wherein the other of said electrodescomprises a metal foil electrode selected from the group consisting ofgadolinium foil, lead foil, and gold foil.

5. An improved radiation detecting display panel as set forth in claim 1wherein said gas includes a noble gas.

6. The panel of claim 5 wherein said gas is a mixture of a gas selectedfrom the group consisting of hydrogen and nitrogen with a gas selectedfrom the group consisting of helium, neon, and argon.

. 7. The panel of claim 5 wherein. said gas is xenon.

8. An improved radiation detecting display panel is set forth in claim 1wherein said voids form a geometric pattern of voids in said platehaving voids.

9. An improved radiation detecting display panel as set forth in claim 1wherein said voids form a random pattern of voids in said plate havingvoids.

10. An improved radiation detecting display panel as set forth in claim1 wherein said first and second plates are relatively opaque toultraviolet radiation and transparent to visible radiation.

11. An improved radiation detecting display panel as set forth in claim1 wherein said source of electrical potential comprises a directcurrentsource.

12. An improved radiation detecting display panel as set forth in claim1 wherein said source of electrical potential comprises an alternatingcurrent source.

13. The panel of claim 12 wherein said alternating current source is apulsed RF source having a carrier frequency in the range 38 kHz to kHz.

14. A display panel as set forth in claim 1 wherein one of said firstand second plates further includes a layer of heavy metal.

15. A display panel as set forth in claim I wherein one of said firstand second plates further includes a layer of ultraviolet photonproducing phosphor.

16. A display panel as set forth in claim 1 wherein one of said firstand second plates comprises leaded glass.

17. A display panel as set forth in claim 1 wherein one of said firstand second plates has a resistive layer overlying said conductivecoating.

1. In a radiation imaging system including a source of radiation forirradiating an object to be imaged and radiation detecting display meansreceiving radiation which has interacted with said object, an improvedradiation detecting display panel comprising: first and second radiationtransmissive fluid impervious plates oriented generally parallel to oneanother and spaced apart; a continuous unitary conductive coatingapplied over substantially the entire area of the interior surfaces ofeach of said plates to form first and second electrodes, at least one ofsaid electrodes being light transmissive; a plate having generallycylindrical voids therein extending therethrough for the entirethickness thereof placed between and generally parallel with saidelectrodes; enclosure means for sealing in gas-containing relationshipat least the region between said first and second plates and forcontaining a gas therein; and a source of electrical potential coupledto said first and second electrodes and producing an electric fieldtherebetween.
 2. An improved radiation detecting display panel as setforth in claim 1 wherein one of said electrodes comprises a metal oxidefilm.
 3. The display panel of claim 2 wherein said metal oxide filmcomprises tin oxide.
 4. The display panel of claim 2 wherein the otherof said electrodes comprises a metal foil electrode selected from thegroup consisting of gadolinium foil, lead foil, and gold foil.
 5. Animproved radiation detecting display panel as set forth in claim 1wherein said gas includes a noble gas.
 6. The panel of claim 5 whereinsaid gas is a mixture of a gas selected from the group consisting ofhydrogen and nitrogen with a gas selected from the group consisting ofhelium, neon, and argon.
 7. The panel of claim 5 wherein said gas isxenon.
 8. An improved radiation detecting display panel is set forth inclaim 1 wherein said voids form a geometric pattern of voids in saidplate having voids.
 9. An improved radiation detecting display panel asset forth in claim 1 wherein said voids form a random pattern of voidsin said plate having voids.
 10. An improved radiation detecting displaypanel as set forth in claim 1 wherein said first and second plates arerelatively opaque to ultraviolet radiation and transparent to visibleradiation.
 11. An improved radiation detecting display panel as setforth in claim 1 wherein said source of electrical potential comprises adirect current source.
 12. An improved radiation detecting display panelas set forth in claim 1 wherein said source of electrical potentialcomprises an alternating current source.
 13. The panel of claim 12wherein said alternating current source is a pulsed RF source having acarrier frequency in the range 38 kHz to 120 kHz.
 14. A display panel asset forth in claim 1 wherein one of said first and second plates furtherincludes a layer of heavy metal.
 15. A display panel as set forth inclaim 1 wherein one of said first and second plates further includes alayer of ultraviolet photon producing phosphor.
 16. A display panel asset forth in claim 1 wherein one of said first and second platescomprises leaded glass.
 17. A display panel as set forth in claim 1wherein one of said first and second plates has a resistive layeroverlying said conductive coating.